In-ground swimming pools made of glass fiber-reinforced plastic ("figerglass") or similar light weight materials have been used since at least as early as the late 1950s. The earliest pools of this general type were manufactured in sections which were mechanically fastened and chemically cemented together in the field. Later, sometime in the 1960s, another type of fiberglass pool came into use which consisted of a number of small, modular, fiberglass panels which were bolted together with the use of gaskets to achieve a waterproof shell. Presently, the most popular fiberglass pools in use are either of one-piece construction or have two or more large sections bolted together and gasketed and assembled on the site. Large pools are sectionalized because of the difficulty of transporting fiberglass shells larger than about 12 feet by 28 feet over the highways.
Fiberglass or other light weight swimming pools have not received widespread popular acceptance, and fiberglass pools which have been installed have suffered a high incidence of failure after or during installation. One reason for these failures is the tendency of such pools to float in the earth excavation as a consequence of hydrostatic pressure from ground water or surface water outside the pool shell. The dead weight of a fiberglass pool shell is exceedingly light compared to pool shells made of concrete, steel or other popular swimming pool materials. This increases the danger of floating the shell during construction or whenever it might be drained for servicing at a later date.
A swimming pool presents a unique construction hazard any time that ground water (water table) or rain water flowing into the excavation reaches a point on the outside of the shell at which the weight of the water displaced by the pool equals the dead weight of the pool shell. The shell is then subject to floating. This is a serious problem during construction. It is not at all unusual to float pools before they are completed and filled with water. When this occurs, the pool shell must be removed from the excavation, the excavation must be drained and reshaped, and the pool shell reinstalled.
In the case of fiberglass pool shell constructions, most designers depend on the weight of the concrete deck or walkway around the pool to keep it from floating in the event that the pool must be drained after completion, the concrete walkway acting as ballast to oppose hydrostatic uplift. This is unsatisfactory. First, the walkway usually does not provide enough dead weight to keep the empty pool shell static. Second, few if any fiberglass pool shells have enough structural integrity to withstand inverse loading to this degree without "oil canning" or "buckling", which results in damage to the pool shell.
The installation of pool shells of prefabricated sectional construction, whether the pool sections are of fiberglass or of other suitable material, has presented certain problems. Prior to the present invention, the usual practice has been to support the walls of the sectionalized pool shells during and after installation by A frames, X frames, or tie-backs to concrete "deadmen" embedded in the ground. Such supports have limited capacity to withstand loading on the pool shell, particularly during backfilling with conventional backfill material, such as sand and water, stabilized soil, cement, or small rock. During such backfilling, the pool walls cannot be maintained vertical by the previously used support arrangements unless the backfill material is introduced very carefully and no hydraulic puddling or mechanical compaction is done to the backfill material.
Most prior bracing systems for sectionalized pools also require that concrete be poured at the base of the walls encasing the lower elements of the bracing system and the bottom of the walls. Use of this technique causes a delay of at least one day in construction time while the concrete takes its initial cure. Periodic shortages of concrete, delivery delays and scheduling problems also compound production delays.
Because the backfill material cannot be adequately compacted when conventional bracing systems are used, decks and walkways around the pool may settle and crack as the backfill material under the deck settles and consolidates after the pool is completed. This is not only unsightly but frequently causes damage to the pool walls when such settling occurs.
The previously used bracing systems for sectionalized pools are made up of many parts and require a multiplicity of hardware and fastening devices which require a great deal of work time in the field to assemble and to attach to the walls. Furthermore, until the concrete encasement around the outside of the walls has been poured and has taken its initial set, these bracing systems require temporary bracing and constant adjustment and re-adjustment to hold the walls in place.